Badger, for what it is worth, I think "pun" is correct too. If you follow Shaney's argument and then change the "i" to a "u" as in the clue (change of heart), it equals pun, which is a wordplay. It fits the clue entirely.
Of course, I assumed essentially referred to middle letter and was thinking boatmsn the setter might want a pen but your answer is better. Thanks for the speedy response
Badger, for what it is worth, I think "pun" is correct too. If you follow Shaney's argument and then change the "i" to a "u" as in the clue (change of heart), it equals pun, which is a wordplay. It fits the clue entirely.
Thanks infomaniac, still haven't put it in yet and dithering like a good 'un! My partner likes the ATM answer now I've read it out. I think wordplay is the definition too so I'll go with that. Let's hope the crossword ed explains in his next article
Thanks again peeps